The present invention relates generally to data communications networks and more particularly to an Available Bit Rate (ABR) flow control system for regulating the allocation of available bandwidth within an Asynchronous Transfer Mode (ATM) network.
Efficient informational flow control has been an important consideration in the research and design of high speed communications networks. The ATM Forum has recently standardized rate-based flow control for best effort traffic in asynchronous transfer mode (ATM) networks. Flow control processing varies a sender""s allowable rate of information transfer in response to feedback from the network within which the information is being transferred. In general, there are two standardized types of transfer, viz. explicit forward congestion indication (EFCI) and relative rate (RR) marking. If a network is not congested, the session""s source of the information being transferred is allowed to increase the rate at which the information is sent thereby taking greater advantage of available bandwidth. When slight congestion is detected, the rate is maintained at current value (RR). When more congestion is present, the rate is reduced. Typically the sending rate of a session during which information is being transferred will oscillate around a desired operating level.
A session with a short propagation delay receives and reacts to feedback from the network much faster than a session with a long propagation delay. This is the fundamental reason which causes an unfair allocation of available bandwidth within an ATM network, i.e. closer nodes will be granted bandwidth at a disproportionate rate relative to nodes which are located a greater distance away. The sending rate for an information packet is decreased if one of the nodes along its path is congested. That xe2x80x9cgreater distancexe2x80x9d information transfer is therefore at a disadvantage with respect to sessions traversing a single xe2x80x9chopxe2x80x9d, or relatively fewer xe2x80x9chopsxe2x80x9d between source and destination nodes. This results in what is known as a xe2x80x9cbeat downxe2x80x9d problem where long-haul connections are starved.
One solution to this problem has been to use xe2x80x9cexplicit ratexe2x80x9d methods where switches are more intelligent and can compute an estimate of the allowable rate for each session. However, such switches are considerably more complex to implement, especially when the switches are targeted for high speed operation.
Therefore there is a need for an improved methodology for determining and assigning allocations of available bandwidth for data transfers within ATM networks.
A data transfer flow control system for a packet ATM communications system includes a plurality of nodes interconnected by transmission links. Available bandwidth allocation for data packets or cells is improved by fixing the sampling period and establishing a xe2x80x9cNrmxe2x80x9d parameter as the product of an allowable cell rate and the sampling period. The parameter xe2x80x9cNrmxe2x80x9d is related to the number of data cells being transmitted between resource management cells in a transmission session, and is set to a number independent of round trip time between source and destination nodes, but varies with the allowable cell rate (ACR).